The present invention relates to a game racket, in particular to a racket having a string suspension system.
Contemporary game rackets such as those used for playing tennis, typically are made of lightweight high strength composite materials such as graphite, super graphite, and titanium to name a few. Some of the most advanced rackets are as light as seven ounces. The superior strength to weight ratio of these space age materials has made it possible to enhance the hitting quality of rackets significantly.
Rackets today have larger xe2x80x9csweet spotsxe2x80x9d.In other words, the area of optimum response on the stringed surface is larger than those used previously. Contemporary rackets have been made stiffer and more powerful than ever before. Power has been increased further by making the rackets bigger and longer and yet they remain lighter than ever. Unwanted vibration and shock common to typical racket construction, is being dampened and attenuated by a number of partially successful means.
Yet in spite of the many improvements offered by innovations over the years, a vast majority have been limited by the inherent nature of the standard stringing system. As defined in Bothwellxe2x80x94U.S. Pat. No. 5,458,331 a major drawback common to previous racket improvements is a xe2x80x9cfixed nodexe2x80x9d stringing system. In the fixed node system the string is laced and/or secured directly to the frame and is partially responsible for the limited size of the sweet spot and the lack of rebound near the edges of the stringed surface. The fixed node configuration is also responsible for direct transfer from the string to the frame of undesirable vibrations and shock from ball impact. Consequently, any attempt to enhance the sweet spot or to improve shock attenuation in a conventional racket is limited by the nature of this stringing system. Fixed node stringing has remained primarily an assumed standard in the history of racket design and construction.
Many reasonable improvements of the fixed node type racket can be found. In U.S. Pat. No. 3,999,756 (by Head) the area of the optimum response on the strings simply is increased by making the stringed surface itself bigger. In U.S. Pat. No. 4,165,071 Frolow improves the sweet spot by modifying the balance and swing weight of the frame. Both however are of the fixed node type and are limited in scope as such.
In U.S. Pat. No. 5,332,213, Klose increases the maximum elastic response of the stringed surface with enlarged string holes which permit the string to move more freely about its fixed node. In U.S. Pat. No. 5,419,963, Kuebler describes a string with a gradually decreasing diameter from its fixed node at the frame to the center of the stringed surface. The thinner middle portion of the string increases its maximum elastic length to improve the sweet spot.
Since the abandonment of wood rackets, shock attenuation has been a major issue in racket design. An inherent inability of graphite composites to attenuate shock in contemporary rackets is aggravated by both the xe2x80x9ceggshellxe2x80x9d like construction of the new super light frames and the ill effects of fixed node stringing. The hitting quality is akin to something made of tin. In fact most rackets currently under 9 ounces have vibration damping handle designs to dampen shock and to add a solid feel to the hollow hitting quality.
Although most shock attenuation methods rely on a post reaction approach, whereby impact shock in the frame is assumed to be a pre-existing condition, there are some that have relied on a pre-reaction approach. A pre-reaction approach does not assume that shock is a pre-existing condition. It attempt to attenuate shock prior to its transfer from the striking surface to the frame.
An early example of this is illustrated by Ryderxe2x80x94U.S. Pat. No. 1,558,507. The stringed surface of the Ryder racket is attached directly to a pneumatic tube which defines its perimeter about the head. By joining the strings with the tube, isolation of the stringed surface from the frame is achieved. Ryder proposes to enhance the liveliness of the strings by securing the tube to the frame with springs. By today""s design standards, the racket of Ryder is inefficient and its array of fittings is complicated and difficult to employ practically.
Another pre-reaction method of shock attenuation and performance enhancement is described in Haythornwaitexe2x80x94U.S. Pat. No. 4,613,138 where a ductile connection between the string and frame is provided by a flexible membrane. As in Ryder, the strings are attached to the membrane with mechanical loops. Manipulation of the tensile state of the membrane, alters its xe2x80x9cspring energyxe2x80x9d and therefore its elastic response and that of the strings. Though the idea is sound the achievement is marred by the mechanical spring assembly located in its handle and the difficulty of its integration with existing racket conventions and methods of fabrication.
Another effort to improve upon fixed node stringing with a pre-reaction approach to racket performance enhancement exists in the form of Maynardxe2x80x94U.S. Pat. No. 4,772,021. Maynard provides a ductile connection of the entire string-bed to the head by means of an inflatable rubber tube. The isolated string-bed offers dramatically reduced shock transfer and improved response of the stringed surface. Its inner frame of the fixed node type however, requires a redundant structure, making the racket heavy, unwieldy and difficult to integrate with current racket conventions. An approach similar to Maynard is Lanctotxe2x80x94U.S. Pat. No. 5,197,732 in which a stringed hoop of the fixed node type is isolated from the frame and held in place by a fluid matter. Some of the best qualities of string isolation are attained, but the redundant structure and the density of the fluid matter required make the racket too heavy.
A most effective pre-reaction solution to fixed node stringing is described by Bothwellxe2x80x94U.S. Pat. No. 5,458,331 in which the woven string-bed of the racket is isolated from the frame by air cushions and is referred to as suspended node stringing. The redundant structure of Maynard is avoided in Bothwell by allowing the tensile load of the string loop carriers to bear on outer facing surface of the cushions. The ductile connection of the strings and frame afforded by the suspension system of Bothwell, improves the area and responsiveness of the sweet spot. Suspended node stringing is unique in its ability to be adapted to accepted racket conventions and methods of manufacture. It represents a fully integrated attenuation method that isolates impact shock at the string bearing point before its transfer to the frame.
The preferred embodiment of this suspension system for a game racket offers most of the performance enhancements of U.S. Pat. No. 5,458,331 but in a simplified manner that is easier to produce. In this version, an isolating gasket is used to isolate the stringed surface from the frame. The resulting string suspension system has all of the qualities of suspended node stringing as defined by Bothwell, but without the inherent difficulty of a fluid tight system.
The ductile connection of the string to the frame in the present invention results in an increase in area of the sweet spot. The degree of enhanced string responsiveness is a function of the physical characteristics of the isolating matter. A compressible matter will decrease the rebound differential from the strings midpoint to its end, making the string more responsive nearer the edge of the stringed surface. In the suspended node configuration, the resiliency of the isolating matter serves to propel the ball with accelerating velocity as it leaves the strings and the compressibility of the matter determines the degree of improved elastic response and dwell time of the ball on the strings. This ability of the suspension system to provide xe2x80x9choldxe2x80x9d on the ball, is a dramatic improvement over the playing quality of a typical racket.
By isolating the string from the frame with a lightweight isolating matter, shock attenuation occurs between the string and frame immediately adjacent to the impact area. The transfer of impact shock to the primary frame is dramatically reduced depending in part on the energy absorbing characteristics of the isolating material. The dampening action of the gasket adds solidity and substance to the hitting quality of the lightest frames. A shock attenuator in the handle or laced through the strings is no longer necessary.
In suspended node stringing, the hitting quality of a racket can be modified by changing the physical properties of the isolating matter. Manipulating the volume and pressure of an air gasket as described by U.S. Pat. No. 5,458,331 will change the hitting quality of a racket. The hitting quality of the racket in the present invention can be controlled by the degree of compressibility or resiliency of the isolating matter. A high density, high impact resistant material would provide a more solid, firmer feel on the ball than the softer feel that a lower density, more compressible substance would give. Other types of materials would likely produce a variety of hitting qualities. An ability to modify the playing quality of a racket by changing the gasket provides a desirable flexibility that recreational players and professionals alike will appreciate.
There can be no doubt about the positive effects of suspended node stringing. The ability to flexibly connect the string and frame coupled with the capacity to precisely control that ductility in a fully integrated approach is a major step in the evolution of string isolation in racket design. That the technology is here represented in a manner that simplifies its construction is a significant step in its path to manufacture.
Accordingly, it is an object of the present invention to provide a game racket with an improved performance.
Another object of the present invention is to provide a particular (e.g., ductile) connection between the string and the frame. It is another object of the present invention to employ a suspended node stringing arrangement, e.g., in a mass produced manner.
A further object of the present invention is to improve a rebound towards a perimeter of the stringed surface and thus to expand the sweet spot. Another object of the present invention is to attenuate an impact shock and a vibration before its transfer from the string to the frame.
Another object of the present invention to isolate and insulate the stringed surface within the head of a racket. A still further object of the present invention is to provide a string suspension system utilizing, e.g., a pressure resistant lightweight isolating material such as foam, silicone, gel, elastomeric chord, etc.
According to the present invention, a racket includes a frame, at least one string and a particular portion. The frame includes a handle portion and a head portion. The string is connected to the frame to provide a string tension. The particular portion is composed of a non-fluid material and disposed on the frame. The particular portion cooperates with the at least one string and is designed to reduce the string tension of the string upon a deflection of the string. The particular portion compresses when the string tension of the at least one string increases.